USED FOR INDICATING ALTITUDES. 45f 



various standard metres proved the accuracy of Hassler's method of comparison. 

 But as the yard of the Troughton scale had been accepted as the standard of length 

 of the United States (see Report on Weights and Measures, by Prof. Bache, 1857) 

 it seemed advisable to call it, as is done in the Coast Survey Reports, the American 

 yard, and its subdivisions, the American foot and inch, and to consider it as a new 

 standard similar to, but not identical with, the English imperial standard. ( Coast 

 Survey Report for 1853.) 



In 1856, however, two copies of the new British standards, viz., a bronze stand- 

 ard, No. 11, and a wrought-iron standard, No. 57, were presented by the British 

 government to the United States. A series of elaborate comparisons of these new 

 standards with the Troughton scale of 82 inches were made from 1876-1878 by 

 Prof. J. E. Hilgard, now Superintendent of the Coast Survey, the results of which 

 were published in 1880, in Appendix No. 12, of Report for 1877. These researches 

 prove that, taking into account the influence of the nature of the material of the 

 standards, and using new, and more correct, coefficients for expansion by heat to 

 reduce them to the same temperature, no material difference is found to exist 

 between the American yard on the Troughton scale and the English imperial yard ; 

 only the Troughton scale at 62 F. is 0.00083 inch longer than the imperial yard at 

 62 F. ; or, otherwise expressed, the mean yard of the United States at 59. 62 F. 

 is equal to the British standard yard at 62 F. 



In confirmation of this conclusion it is well to remark that the value of the metre 

 derived from Hassler's comparisons and reduced to 62 by Prof. Bache, as above 

 stated, when properly corrected with the new elements, stands as follows : 



Hassler's value of the metre reduced to 62 F. = 39.36851 Eng. inches. 



Correction for difference in rate of expansion -f- .00109 " 



Correction for excess of Troughton scale in one metre -f .00090 " 



Hassler's comparison corrected reduction = 39.37050 " 



which is almost identical with Clarke's value. 



Thus the American yard, as a distinct one from the English standard yard, is 

 happily abolished. In consequence the tables for the conversion of the American 

 yards and feet have been omitted in the present edition. 



5. The Klafter of Vienna is a silver line let into a prismatic bar of iron, on which 

 the length of the klafter was engraved by Voigtlander. It has its normal length at 

 13 Reaumur, and was declared by law, in 1816, the standard Klafter of Vienna. 

 On the same silver line the French toise is marked, from the standard toise sent, in 

 1760, by La Caille and La Condamine to the Observatory of Vienna. Comparisons 

 made by Prof. Stampfer with this standard gave for its value in metres 1 Klafter of 

 Vienna = 1.8966657 metre, which value was universally used until about 1850. 



New comparisons of the Vienna standard with various French standards deposited 

 in the Russian Imperial Observatory, made in 1850 by the Astronomer W. Struve, 

 with the utmost care and scientific precision, gave as a result 



1 Klafter of Vienna^ 1.8964843 metre, 



which value is now admitted as the most reliable. (Memoirs of the Austrian 

 Academy of Sciences, vol. v. p. 117, and Sitzungs Berichte, Mathemat. Natur- 

 E 11 



